(1) Field of the Invention
The present invention relates to a transmission for a tractor and particularly to a power takeoff line in the transmission for transmitting an engine output to a working implement attached to the tractor.
(2) Description of the Prior Art
Drive transmission to a working implement such as a rotary plow attached to the tractor is disclosed, for example, in U.S. Pat. No. 4,565,102. As in this patent, the engine output generally is transmitted to the working implement through a main clutch and a power takeoff clutch. However, when the tractor engages in a plowing operation for example, the power takeoff line having the above construction allows an overload to fall on the engine suddenly when the working implement encounters a very hard soil or when its plowing depth suddenly increases for some reason. In the worst case such an overload may result in an engine failure. In order to avoid such an inconvenience, a proposal has been made in the Japanese utility model application laid open under No. 55-41695 in which the power takeoff line includes a safety clutch for automatically breaking drive transmission when a torque exceeding a predetermined value takes place. However, although the proposed constuction is capable of avoiding the engine failure in spite of the excessive torque, the rotary plow is caused to stop temporarily and leave an unplowed patch in the field.